Study: Moon is made up of early Earth's mantle

Scientists say the moon was formed by a
high-energy impact which vaporized most of the Earth and created a
massive magma atmosphere.

Brooks Hays

New research suggest the moon was formed from a high-energy
impact that vaporized much of Earth. Photo by Dana Berry/SwRI

New isotopic analysis confirms the moon was forged from proto-Earth's mantle several billion years ago.

Scientists say their latest findings, detailed
in the journal Nature, finally settle the debate over whether Earth or
its ancient impactor formed the moon.

Previously, the most popular explanation for
the birth of the moon was the giant impact model, which suggested the
moon was formed by a grazing impact between a Mars-sized body and the
Earth. The giant impact model explained a variety of the moon's physical
characteristics, including its size and rotation.

But the model suggested the moon was mostly
formed by the material of the impactor. Isotopic analysis suggested the
opposite, with lunar and Earth samples revealing nearly exact
concentrations of the three oxygen isotopes.

Isotopes serve as fingerprint-like chemical
signatures of the solar system's many bodies. The chance Earth's
impactor featured the same isotopic composition was too small to
consider.

"These are the most precise measurements we
can make, and they're still identical," Washington University in St.
Louis geochemist Kun Wang said in a news release.

So scientists went back to the drawing board,
attempting to augment the giant impact model in a way that could explain
the isotopic similarities of the Earth and its moon.

One hypothesis suggested a silicate vapor
atmosphere spread about the impacted Earth and vaporized the impactor,
allowing the exchange of materials between the Earth and its impactor.

"They're trying to explain the isotopic
similarities by addition of this atmosphere," Wang said, "but they still
start from a low-energy impact like the original model."

Simulations showed such a scenario would take
too long to account for the isotopic similarities, as the moon would
have formed fairly quickly from the condensed magma in the wake of the
impact.

A second hypothesis proposed a high-energy
impact which vaporized most of the Earth and created a massive magma
atmosphere, thoroughly mixing the materials of Earth and its impactor.
It is from this haze of melted rock that the Earth reformed and the moon
was born.

New analysis of potassium isotope levels in lunar and terrestrial rocks support the high-energy impact theory.

"The enrichment of the heavy isotope of
potassium in lunar rocks compared with those of the Earth and chondrites
can be best explained as the result of the incomplete condensation of a
bulk silicate Earth vapour at an ambient pressure that is higher than
10 bar," Wang and his colleagues wrote in a paper, newly published in the journal Nature.

The enrichment of lunar rocks with heavier
potassium isotopes can't be explained by a silicon vapor atmosphere,
researchers report.

"Our K isotope result is inconsistent with the
low-energy disk equilibration model," researchers wrote, "but supports
the high-energy, high-angular-momentum giant impact model8 for the
origin of the moon."

Study: Moon is made up of early Earth's mantle
Reviewed by Chidinma C Amadi
on
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